In recent years, the consumption of silver halide photographic light-sensitive materials has been and is increasing steadily. Accordingly, the processing number of silver halide photographic light-sensitive materials increases, leading to the demand for even more rapid processing. i.e., for the increase in the processing number of light-sensitive materials per unit time.
The above-mentioned tendency is seen also in the field of light-sensitive materials for X-ray use, for example, medical radiographic films. That is, the significant increase in the number of diagnoses due to the strict observation of periodical medical checks, etc., and the increase in the medical inspection items for the purpose of making the diagnosis even more correct leads to the increase in the number of radiographing films.
On the other hand, there is also the necessity to inform medical examinees of diagnostic results as soon as possible; that is, there are strong demands for more rapid processing than ever before to immediately provide the processed results for the diagnosis. Particularly the angiography, the radiographing carried out in the midst of a surgical operation, and the like, essentially need the viewing of the finished radiographic image in no time.
In order to meet the above wishes of the medical field, it is necessary to further speed up the processing of X-ray films as well as to promote the automation of the diagnostic procedure (including radiographing and transportation).
However, if a rapid processing of a film takes place, it tends to bring about the problems that the film (a) shows an inadequate image density (the sensitivity, contrast and maximum density are deteriorated), (b) is not completely fixed, (c}is not sufficiently washed, and, (d) is not completely dried. And the incomplete fixation and washing of a film cause the film to be discolored during the storage thereof, thus deteriorating the image quality.
One way to solve these problems is to reduce the amount of gelatin. However, the reduction of the amount of gelatin gives rise to various other problems: For example, (1) such troubles as coating marks, coating streaks, etc., tend to appear in the coating of a silver halide photographic light-sensitive material, (2) where the film is rubbed with each other or with other materials, the rubbed part, after being developed, tends to have a higher density than that of the other parts; the so-called scratch darkening, (3) when the film, after being bent, is imagewise exposed and then developed, the bent part tends to have a lower density than that of the other parts; the so-called pressure desensitization, and (4) since a developer solution can permeate and diffuse fast into the layer, the development becomes active, causing the developed silver to become coarse, so that the graininess looks roughened.
It has been so difficult to solve these problems to date that it was unable to reduce the amount of gelatin in conventional films.
The advent of a super-rapid processing system is desired as has been described above. The "super-rapid processing" herein means a processing by an automatic processor of which the total time required for the overall processing from the point of time when the leading end of a film is inserted into the processor and transported through the developer bath, first cross-over rack, fixer bath, second cross-over rack, wash water bath, third cross-over rack, and drying rack up to the time when the trailing end of the film gets out of the drying section in other words, the quotient (sec.) obtained after dividing the whole length of the processing line (m) by the line transport speed (m/sec )]is from 20 seconds to 60 seconds.
The reason why the cross-over time is to be included in the processing time, although well-known to those in the art, is because it is considered that, even in the cross-over passage, the preceding process liquid is present in the gelatin layer to have the processing action substantially go on.
Japanese Patent Examined Publication No. 47045/1976 describes the importance of an amount of gelatin used in rapid processing, wherein the total processing time including the cross-over time is described to be from 60 to I20 seconds. This processing time, however, is unable to satisfy the recent demand for super-rapid processing.
Also, particularly as the medical X-ray checks increase in recent years, the international opinion as well as the medical world demands strongly the reduction of exposure dose. In order to meet this demand, fluorescent intensifying screens, intensifying screens, devices or means such as fluorescent screens, X-ray image intensifiers, etc., are used. The improvement of these devices or means and the increase in the sensitivity of photographic light-sensitive materials for X-ray use in recent years are remarkable. On the other hand, high-precision radiographic technology is demanded for more precise medical checks. Since the larger the amount of X-ray irradiation the higher the precision, a radiographing technique for irradiating a large dose has been developed and a large-capacity X-ray generator has also been developed therefor. However, such the radiographing technique requiring a large dose is unacceptable because it runs rather counter to the foregoing demand for the reduction of exposure dose. Accordingly, the radiographic field requires a high-precision photographing technique which uses a small exposure dose, and therefore longs for the development of a photographic light-sensitive material capable of giving precise images with a small X-ray dose; i.e., a still higher-speed photographic light-sensitive material.
There are a large variety of techniques to increase the speed of a photographic light-sensitive material with its silver halide grain size remaining intact; that is, sensitizing methods. If a proper sensitizing technique is used, a light-sensitive material may be expected to have its speed increased with its grain size remaining as it is; i.e.. with its covering power kept on. Many are reported as the technique, including, e.g., methods of adding to an emulsion a development accelerator such as a thioether, methods for the supersensitization of a spectrally sensitized silver halide emulsion by use of an appropriate combination of sensitizing dyes, techniques of improving optical sensitizers, and the like.
These methods, however, are not always widely usable in high-speed silver halide photographic light-sensitive materials. That is, the silver halide emulsion for high-speed silver halide photographic light-sensitive materials is chemically sensitized to an utmost possible extent, so that, if any of the above methods is applied, a light-sensitive material tends to be fogged during the storage thereof. In addition, in the medical radiographic field, those conventionally used regular type which were sensitive to wavelengths around 450 nm are out-of-date, and are now replaced by orthochromatic-type light-sensitive materials sensitive to wavelengths of from 540 to 550 nm. Those thus sensitized are sensitive to a wider wavelength region and also have a higher speed than conventional ones so as to allow the reduction of an exposure dose, thus making smaller the influence upon the human body. Thus, the dye sensitization is a very useful sensitizing means, but has lots of problems yet to be solved; for example, there still remain problems that no adequate sensitivity can be obtained depending on the type of the photographic emulsion used, and so forth.
Also, there are cases where various mechanical pressure applied prior to exposure causes a pressure sensitization trouble (desensitization marks found on a light-sensitive material at the time of its development, caused by mechanical pressure applied before exposure). For example, a medical X-ray film sheet, since its size is large, sometimes bends from its supported portion due to its own weight to cause a pressure desensitization trouble which tends to appear in the form of so-called knick marks.
Also, nowadays medical X-ray photographic systems such as automatic exposure and processing apparatus provided with mechanical transport systems are widely used. In these apparatus, mechanical force is applied to the film in transit, and tends to cause both the foregoing pressure-darkening and pressure desensitization troubles especially in the winter season or in a dry place. Such phenomena will probably constitute a serious hindrance to diagnoses. Particularly it is well-known that the larger the grain size of and the higher the speed of a silver halide photographic light-sensitive material the more easily does the pressure desensitization trouble occur.
There are those methods using. e.g., thalium or dyes for the purpose of improving so as not to cause the pressure desensitization as described in U.S. Pat. Nos. 2,628,167, 2,759,822, 3,455,235, 2,296,204, French patent No. 2,296,204, and Japanese Patent Publication Open to Public Inspection (hereinafter referred to as Japanese Patent O.P.I. Publication) Nos. 107129/1976 and 16025/1975, and the like, but some of them are not adequate in the degree of the improvement, some produce a conspicuous dye stain, and some others can not necessarily be considered to derive adequately the nature of a high-speed silver halide photographic light-sensitive material utilizing chiefly the ordinary surface high sensitivity of a large average grain size.
On the other hand, many attempts have hitherto been made to improve silver halide photographic light-sensitive materials so as not to cause the pressure desensitization by changing the physical property of the binder thereof. Such attempts are found in, e.g., U.S. Pat. Nos. 3,536,491, 3,775,128, 3,003,878, 2,759,821 and 3,772,032, Japanese Patent O.P.I. Publication Nos. 3325/1978, 56227/1975, 147324/1975 and the like. However, these techniques, although improving light-sensitive materials in respect of the pressure desensitization, deteriorates conspicuously the physical properties of the binder such as dryability, scratch resistance, etc., and thus cannot improve light-sensitive materials fundamentally.